The gerotor is a special positive displacement mechanism that is capable of delivering a known, predetermined, quantity of fluid in proportion to its revolving speed. A gerotor set can also be considered as a special form of an internal gear transmission mechanism, consisting of two main elements: (I) an externally toothed inner rotor or gear; and (II) an internally toothed outer ring or gear, as best seen in both FIGS. 1A and 1B. The inner rotor of any gerotor set has one less tooth than its adjoining outer ring, and the inner rotor and the outer ring possess different centers with a fixed eccentricity. When both the inner rotor and the outer ring are free to rotate with their fixed centers, the rotation of the inner rotor will force the outer ring to rotate in the same direction. However, when the outer ring is fixed, rotation of the inner rotor will cause the center of the inner rotor to orbit in the opposite direction, with this motion being similar to that of a planetary gear revolving around the inside of a ring gear. Therefore, depending on how a gerotor set is used at a specific actual application, the gerotor set can be either non-orbital or orbital. Non-orbital gerotor sets, for example, are commonly used in high speed gerotor pumps, while orbital gerotor sets, for example, are typically used for low speed gerotor motors.
In addition, a gerotor set can be classified as an externally generated rotor (EGR) set (FIG. 1A) or an internally generated rotor (IGR) set (FIG. 1B). The inner rotor “teeth” of an EGR gerotor set are specially shaped lobes that are in contact with circular arcs/rollers of the outer ring at all times when the inner rotor revolves. Vise versa, the outer ring “teeth” of an IGR gerotor set are specially shaped lobes that are in contact with the noted circular arcs/rollers of the adjoining inner rotor at all times when the inner rotor revolves. Each volume chamber of any gerotor set is separated by continuous contact between the lobes and circular arcs/rollers, with the volume of each chamber changing as the inner rotor revolves. The rotary mechanism of the gerotor set, by virtue of its continuous chamber volume change, can be used as a positive displacement fluid controller in mechanisms such as hydraulic pumps, motors, steering units and rotary engines, etc. Gerotor mechanisms are currently recognized as the most popular working power elements for hydraulic pumps and motors. It is estimated that more than 50 million gerotor pumps and more than 2 million gerotor motors are manufactured yearly, worldwide, because gerotors provide a good combination of compact size and low manufacturing cost, with these noted quantities being much greater than those of any other type of hydraulic pump and motor.
Much effort has been expended to perfect this internal gear mechanism with continuous contact between the inner rotor and the outer ring while using an internal gear set of one-tooth difference. Initially, manufacturers had claimed that it was not practical to tool the gerotor for mass production and it was not until the 1920's that Henry Nichols developed a special profile gear grinder for the inner rotor of the EGR gerotor, with several later generation grinders of this type currently still being in service, albeit, mainly for low-volume special applications.
Both EGR and IGR gerotor sets require high precision manufacturing tools and methods along with very tight dimensional tolerances, particularly on the rotor profile. Currently, two methods are used to machine the external surface of the inner rotor of an EGR gerotor set. The external special profile of an EGR inner rotor can either be ground by a special gerotor grinding machine of the type invented by Henry Nichols or by a multi-purpose profile/form grinder. The inventors of the present invention are unaware of any special grinder that has been developed for grinding the special profile of the inner surface of the IGR outer ring. The only known mass production method currently being used utilizes a very expensive multi-purpose profile/form grinder. FIGS. 2A and 2B, which will be discussed in more detail later, illustrate the current grinding method for generating the internal surface of an IGR outer ring that utilizes a specially profiled grinding wheel installed within a cantilevered column. Due to possible deformation of the noted cantilevered column, during the grinding operation, an IGR rotor, ground via the previously noted internal profile/form grinder, may possibly have mismatch problems near the area where two gear flanks meet as shown in FIGS. 3A, 3B and 3C which will also be discussed in more detail hereinafter.
The patent literature lists a number of apparatuses and methods for grinding the tooth flanks on internally toothed gear wheels that include: U.S. Pat. No. 1,798,059 to Bilgram et al.; U.S. Pat. No. 2,665,612 to Nübling; as well as U.S. Pat. Nos. 3,782,040 and 4,058,938, both to Härle et al. However, none of the prior art methods of gear generation, set forth therein, pertain to the methods set forth in the present invention.